Proceedings World Geothermal Congress 2010 Bali, Indonesia, 25-29 April 2010 The Cachiyacu Geothermal Prospect, Chacana Caldera, Ecuador Bernardo Beate(1), Salvatore Inguaggiato(2), Fabian Villares(1), Stalin Benitez(3) and Silvana Hidalgo(4). (1) Dto. de Geologia, Escuela Politecnica Nacional, P.O. Box 17 01 2759, Quito / Ecuador (2) Istituto Nazionale di Geofisica e Vulcanologia -Palermo, via Ugo La Malfa 1590146, Palermo, Italy (3) Samanes 1ª. Etapa, Manzana 130, Villa 1, Guayaquil, Ecuador (4) Instituto Geofisico, Escuela Politecnica Nacional, Ladron de Guevara E11-253 y Andalucia, Quito, Ecuador [email protected] [email protected] [email protected] [email protected] [email protected] Keywords: Ecuador, geothermal exploration, resurgent the Eastern Cordillera (CR), about 65 km ESE from the caldera, rhyolite dome, hot springs, use of geothermal capital city of Quito. Elevation range from 3200 up to 4100 energy. masl on ragged topography covered with high-altitude grassland and few cloud-forest patches. Climate is cold and ABSTRACT wet for most of the year. There are no people living in Cachiyacu area and there is no road access to it, although Cachiyacu is located at about 65 km ESE of the capital city the villages of El Tambo and Papallacta are 5km and 12 km of Quito, in the high ranges of the Eastern Cordillera at away in NE direction, respectively. A paved highway 4000 masl, on ragged topography in a wet and cold climate. connects these villages with Quito and the Amazon basin. Paved accesss road and high voltage transmission line cross along its northern border; the main load center is Quito. The Earlier work on the assessment of geothermal resources by heat source is the southern part of the resurgent silicic INECEL-OLADE (1980) and by Almeida (1990) and Chacana caldera, which has been persistently active since Almeida et al., 1992, didn’t consider Chacana as a high late Pliocene, producing numerous rhyolitic domes, temperature geothermal resource, although it is taken into andesitic to dacitic lava flows and ignimbrites of high-K account by Beate & Salgado, 2005, and Beate, 2008, which calc-alkaline affinity; latest volcanic activity comprises two prompted the interest of Electroguayas in the area. The large Si-andesite lava flows as recent as 240 yr BP. The 35 actual knowledge is mostly regional geology; recent by 15 km diameter caldera structure is hosted in the vulcanological studies by IG/EPN by Hall & Mothes (2008) Paleozoic-Mesozoic metamorphic basement and is likely have outlined the evolution of Chacana Caldera and its roll controlled by regional NNE-striking strike-slip faults. A hot as part of the Ecuadorean Rhyolitic Province (ERP). Just water–dominated geothermal system, with deep recently, the geochemical base line for the Ecuadorian arc temperatures in excess of 200 °C is assumed to be hosted in has been established, including the Chacana area the late Tertiary to Quaternary volcanic pile filling the (IG/EPN/INGV 2009) caldera and in its lower wall rocks. 30 to 65 °C, highly saline hot springs are common inside the area and its waters In the following sections we present an outline of the belong to the Cl-SO4-alkaline type. Hot spring water along regional geological setting of the Chacana Caldera, a brief a NE-oriented outflow at 5 to 10 km distance, is used sketch of the geology and evolution of the Chacana Caldera mainly for bathing purposes and less for space heating. with emphasis on its southern part and Cachiyacu in Older hydrothermal alteration is widespread in the area. A particular; than we outline the main results of the preliminary geothermal model is proposed in the Cachiyacu geochemical survey on hot spring waters and discuss the area with a self-sealed reservoir and permeability sustained mayor issues of a preliminary geothermal model for by active faults. A comprehensive magnetotelluric survey is Cachiyacu. recommended to locate the geothermal reservoir and to site the first deep drilling targets in Cachiyacu. 2. GEOLOGICAL SETTING Continental mainland Ecuador consists of three distinct 1. INTRODUCTION geomorphologic and geographic regions: the coastal plains The Ecuadorean government has priorized the development or COSTA, the Andes mountain chain or SIERRA and the of renewable sources of energy with the aim to reduce and Amazon basin or ORIENTE; a fourth region comprises the eventually replace the use of fossil fuels for power Galapagos Islands located about 800 km to the W of the generation. This study was funded by Electroguayas, a state coastline in the Pacific Ocean (see fig. 1). owned power generation entity, with the objective to assess the geothermal potential of the Cachiyacu area and prepare The Andes constitute the very backbone of the country. Its a preliminary geothermal model, based on reconnaissance formation is due to multiple accretion since Jurassic times geological and geochemical surveys. Geological work (Aspden and Litherland, 1992; Eguez and Aspden, 1993). It included field mapping and sampling, as well as consists of two parallel NNE-striking mountain chains: a) geochemical assays by ACME Labs, Vancouver-Canada of the Eastern Cordillera or Cordillera Real (CR) which are the most representative rock samples. Geochemical work sublinear belts of Pz-Mz metamorphic rocks intruded by consisted of sampling water from 19 warm and hot springs both, I- and S-type granitoids of early Mesozoic age; and b) as well as bubbling gas and surface waters; geochemical the Western Cordillera or Cordillera Occidental (CO), analysis of the fluids were done at the Istituto Nazionale de which consists of late Mesozoic to early Cenozoic basalts Geofisica e Vulcanologia at Palermo, Italy. and vulcaniclastics, representing accreted oceanic terrains (Hughes and Pilatassic, 2002). These rocks are intruded by The Cachiyacu geothermal prospect is located in the Tertiary granitoids. Both cordilleras have been folded and southern end of the silicic Chacana caldera, on the crest of uplifted and are covered by late Tertiary volcanics. 1 Beate et al. Fig. 1 Geodynamic setting of Ecuador, depicting location of Cachiyacu Geothermal Prospect The Interandean Valley (IAV, see fig. 1) is located between Geodynamic processes in Ecuador since late Oligocene are the two cordilleras and comprises thick late Tertiary to controlled by the near orthogonal convergence between Recent vulcaniclastic and epiclastic sedimentary sequences; Nazca and Southamerican plates, which has generated it is bounded laterally by NS oriented terrain sutures, the regional uplift and crustal faulting and deformation as well Pujili – Calacali suture to W and the Peltetec suture to E, as extensive volcanism (Londsdale, 1978). which continue into Colombia as the Cauca-Patia and Romeral sutures, respectively. Suture-paralell overprinting The compressive tectonic regime formed several active faults, mostly thrust faults, mark the morphology of intramontane basins between the two cordilleras since the actual IAV borders. Miocene. The IAV has been formed as a spindle shaped basin along a restraining bend in a transpressive regime Covering both cordilleras in its northern half, a well since about 6 Ma due to an increase in the coupling of the developed, subduction-related, broad, calc-alkaline Carnegie ridge in the subduction zone (Spikings, 2001; continental volcanic arc extends northwards into Colombia Winkler, 2002; Villagomez, 2002). (Barberi et al., 1988; Hall & Beate, 1991). The arc is of Quaternary age and consists of more than 50 volcanoes, of The northern half of the country is now part of the North which at least 30 are active and four are in eruption or did Andean Block (NAB), which moves at 6-10 mm/yr in NE- so in the last ten years. The southern half of the Ecuadorian NNE direction along regional dextral strike-slip faults Andes shows only extinct volcanic activity, the latest one (Ego, 1993). This active regional fault system enters the being at Quimsacocha caldera at 3.6 Ma (Beate et al., gulf of Guayaquil creating extension and normal faulting 2001); the outset of volcanism is due to the flattening of the (fig.1). It continues northwards along the dextral Pallatanga slab since late Miocene (Gutscher et al., 2000). fault, which cuts both, the Western (CO) and the Eastern Cordillera (CR), as well as the IAV, emerging further N as The Oriente is an extensive sedimentary basin, overlying the Chingual fault at the border with Colombia, where it cratonic basement (Baldock, 1982). Older rocks comprise continues along a NS strike. Jurassic volcanics and batholiths and a Cretaceous carbonatic platform, covered by Tertiary epiclastic This tectonic activity together with the extensive sediments; large NS-striking thrust faults cut the sequence Quaternary volcanism present in the northern Ecuadorean toward its western limit (Tschopp, 1953). Quaternary Andes are the regional setting for the Chacana caldera and alkalic volcanoes are located along the W margin of the the Cachiyacu geothermal prospect. basin in a back-arc setting. 3. GEOLOGY OF CACHIYACU PROSPECT The Costa is the flat region between the Andes and the The Cachiyacu prospect area is located inside the Chacana Pacific Ocean. It comprises a late-Cretaceous to Cenozoic caldera, close to its southern rim and comprises about 100 fore-arc basin underlain by mid to late Mesozoic oceanic km2. The area is flat caldera floor at the site of the hottest crust (Benitez, 1995; Vallejo, 2009). There is no active thermal springs, where it is surrounded by steep caldera volcanism in this area. walls to W, Plaza de Armas dome-flow complex to the S The Galapagos Islands are an active mantle hot spot and the and Yanaurcu and San Clemente felsic domes to E and N, asismic Carnegie ridge (see fig. 1) represents the trace of respectively. In contrast, topography to the E of the the hot spot over the Nazca Plate, which is actively mentioned domes is rugged and difficult.